Bad I2C Port?

Using Arduino Installation & Troubleshooting
#1

I have a board with ~4 I2C devices on it and it was working just fine with code and everything.

I soldered another I2C device on than the whole chip completely froze, stalled in setup(). I removed the chip but the problem stayed, but if I remove all I2C code the rest of the program works, and I could always re-program via USB no issue.

With I2C disabled, I determined that the SDA line was only 1.2V, but after some re-work and testing it suddenly switched to the SCL line, than some time later they both when to 0.5V . Something is pulling the pins low but its not obvious why.

Do you think the I2C port is damaged?

#2

Do you have 3.3K or 4.7K pullup resistors on SCL & SDA?

#3

In this case I went with 10K pull ups, never had an issue up till this point.

I did try to strengthen the pull up by putting I put addition 10K on the lines (net 5K), made no difference.

#4